1. Field of the Invention
The present invention relates to a lithium-ion secondary battery separator and a lithium-ion secondary battery.
2. Related Background Art
Conventionally, polyolefin-based stretched porous films and the like have been in wide use as separators for lithium-ion secondary batteries, while cellulose-based nonwovens and the like have widely been employed as separators for electrolytic capacitors and electric double-layer capacitors. These electrochemical devices are typically those of a winding type and do not require adhesion between electrodes and separators in their manufacturing process in particular.
In multilayer devices such as polymer lithium ion batteries, on the other hand, a technique in which binders for use in electrodes are thinly formed on polyolefin-based separators has been employed in order to enhance the adhesion between the electrodes and separators (see, for example, Japanese Translation of PCT International Application Laid-Open No. 2002-529891 and Japanese Patent Application Laid-Open No. 2004-227972).
In the lithium-ion secondary batteries, olefin-based polyethylene (PE) and polypropylene (PP) have been used in separators, so that the difference between their melting points is utilized for exhibiting a shutdown function, in order to enhance the safety of batteries (see, for example, Japanese Patent Application Laid-Open Nos. 60-136161 and 63-308866).